Plasticization resistance-enhanced CO₂ separation at elevated pressures by mixed matrix membranes containing flexible metal-organic framework fillers

Although precise design has advanced the separation capability of polymer membranes, the inability to maintain their performance under real process conditions involving elevated pressures and moisture has prevented their smooth transition into practical applications. Specifically, plasticization of polymers is a unique challenge to membrane-based CO₂ separation. Herein, we show that the dispersion of a flexible metal-organic framework (MOF) within a polymer matrix allows the retention of high gas separation selectivity even at a transmembrane pressure of 12 bar, which is highly desirable for practical applications involving compressed feed streams. The strong interactions between MOF fillers and polymer matrices reduce the chain mobility of polymer, contributing to the enhanced plasticization resistance. X-ray diffraction (XRD) analysis indicates that channel closure of the flexible MOF in polymer is avoided, also suggesting strong MOF-polymer interactions. Importantly, observation of XRD-detectable phase changes in flexible MOFs is a useful strategy to reveal the interactions between flexible MOFs and the matrices.